The molding of tires, in particular the tread of tires, must satisfy a number of restrictive conditions.
One of these conditions concerns the stripping of the tread sculpturing from the mold, which must impose as little stress as possible on the tire, under the penalty otherwise of causing disturbances, particularly in the reinforcement architecture of the tire. This leads to the preference of so-called "sector" molds, illustrated, for instance, by the disclosure in U.S. Pat. No. 3,779,677, rather than so-called "two part" molds (see U.S. Pat. No. 2,874,405).
Furthermore, it is desirable that, particularly at the level of the tread, there is no burr due to rubber which has been able to flow between two molding elements, for instance between two sectors. For this reason, as a general rule the mold is closed (all sectors adjoining each other) before imposing additional shaping on the raw tire by increase of the pressure prevailing in the vulcanization membrane, which causes the rubber of the tread to penetrate into the elements which mold the tread pattern.
EP Patent Application 0 242 840 describes a completely rigid mold having a peripheral ring of sectors in order to mold the tread, two lateral shells to mold the side walls (outer surfaces of the tire), and a rigid core to mold the inner surface of the tire. The completely rigid design of this mold results in numerous advantages as to the quality of the molded tire since the geometrical shapes obtained are of high quality (excellent circularity in every transverse position). However, the volume molding imposed makes it necessary to satisfy very close tolerances with regard to the volume of the raw blank of the tire.